This invention relates generally to an electrostatographic printer and copier, and more particularly, concerns a cleaning apparatus for removal of residual particles and agglomerates from the imaging surface.
In an electrophotographic application such as xerography, a charge retentive surface is electrostatically charged, and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface from an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charge surface may be imagewise discharged in a variety of ways. Ion projection devices, where a charge is imagewise deposited on a charge retentive substrate, operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during transfer some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom.
A commercially successful mode of cleaning employed on automatic xerographic devices utilizes a brush with soft conductive fiber bristles which have suitable triboelectric characteristics. While the bristles are soft they are sufficiently firm to remove residual toner particles from the charge retentive surface. A voltage is applied to the fibers to enhance removal of toner from the charge retentive surface.
Not all toner and debris is removed from the surface by the brush cleaner. For reasons that are unclear, toner particles agglomerate with themselves and with certain types of debris to form a spot-wise deposition that can eventually strongly adhere to the charge retentive surface. These spots range from 50 micrometers to greater than 400 micrometers in diameter and 5 to 25 micrometers in thickness, but typically are about 200 micrometers in diameter and 5 to 15 micrometers in thickness. The agglomerates range in material compositions from nothing but toner to abroad assortment of plastics and debris from paper. The spots cause a copy quality defect showing up as a black spot on a background area of the copy which is the same size as the spot on the photoreceptor. The spot on the copy varies slightly with the exact machine operating conditions, that cannot be deleted by control of the machine process characteristics.
While attempts were made to eliminate the agglomerate spotting by controlling of extraneous debris within the device this solution has been found difficult if not impossible to implement. Additionally, there was no way to eliminate the formation of agglomerates that the toner formed itself. However, in studying the formation of these spots, it was noted that the spots appeared instantaneously on the charge retentive surface, i.e., the spots were not the result of a continuing nucleation process. It was subsequently noted that newer deposited spots were more weakly adhered to the surface than older spots.
The following disclosure may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 4,989,047 to Jugle et al. discloses a cleaning apparatus for an electrophotographic printer that reduces agglomeration-caused spotting on the imaging surface. A secondary cleaning member, characterized as a thin scraper blade, is arranged at a low angle of attack, with respect to the imaging surface, to allow a maximum shearing force to be applied by the blade to the agglomerates for removal thereof.